A large backhoe excavator (which may hereinafter be called simply “a backhoe”) is provided with a travel base capable of traveling by drive of left and right crawler tracks, a revolving upperstructure mounted for revolution on the travel base and having an operator's cab, and a front working assembly having a boom connected to a front part of the revolving upperstructure, an arm pivotally connected to the boom and a bucket pivotally connected to the arm.
The backhoe excavator is also provided with plural hydraulic actuators for driving the travel base, revolving upperstructure and front working assembly, specifically a right travel motor and a left travel motor as drive sources for the travel base, a swing motor as a drive source for the revolving upperstructure, a boom cylinder as a drive source for the boom, an arm cylinder as a drive source for the arm, and a bucket cylinder as a drive source for the bucket.
Arranged in the operator's cab of the backhoe excavator are plural control devices, specifically a right travel control pedal device for instructing operation (operation direction and operation speed) of the right travel motor, a left travel control pedal device for instructing operation of the left travel motor, a swing control lever device for instructing operation of the swing motor, a boom control lever device for instructing operation of the boom cylinder, an arm control lever device for instructing operation of the arm cylinder, and a bucket control lever device for instructing operation of the bucket.
The backhoe excavator is further provided with a hydraulic drive system for operating plural hydraulic actuators, namely, the right travel motor, left travel motor, swing motor, boom cylinder, arm cylinder and bucket cylinder in accordance with operation of the right travel control pedal device, left travel control pedal device, swing control lever device, boom control lever device, arm control lever device and bucket control lever device. This hydraulic drive system is provided with a hydraulic drive circuit including plural variable-displacement hydraulic pumps capable of serving as hydraulic sources for the hydraulic actuators and directional control valves interposed between said plural variable-displacement hydraulic pumps and said plural hydraulic actuators to control flows of pressure oil between the individual variable-displacement hydraulic pumps and the individual hydraulic actuators. In other words, the hydraulic drive system is configured to control the operation directions and operation speeds of the plural hydraulic actuators by controlling regulators for the plural variable-displacement hydraulic pumps and the plural directional control valves in accordance with the operation of the right travel control pedal device, left travel control pedal device, swing control lever device, boom control lever device, arm control lever device and bucket control lever device.
A large loader excavator (which may hereinafter be called simply “a loader excavator”) is provided, similar to the backhoe excavator, with a travel base, a revolving upperstructure and a front working assembly, aright travel motor, a left travel motor, a swing motor, a boom cylinder, an arm cylinder and a bucket cylinder as drive sources for them, and a hydraulic drive system for controlling operation of these hydraulic actuators.
As the front working assembly of the backhoe excavator and that of the loader excavator are different in digging operation, the arm cylinder and bucket cylinder are arranged on an outer side of the front working assembly in the backhoe excavator while the arm cylinder and bucket cylinder are arranged on an inner side of the front working assembly in the loader excavator. As a consequence, the pivoting directions of the arm and bucket when the arm cylinder and bucket cylinder extend or retract in the backhoe excavator and those of the arm and bucket when the arm cylinder and bucket cylinder extend or retract in the loader excavator are opposite. In addition, the front working assemblies are also different in the manner of control of flow rates suited for the control of operation speeds.
Further, the bucket of the loader excavator is constructed openably and closably. This bucket is provided with an open/close cylinder as a drive source for the opening/closing of the bucket. Arranged in an operator's cab of the loader excavator are an open control pedal device for instructing a bucket-opening operation and a close control pedal device for instructing a bucket-closing operation. The hydraulic drive system of the loader excavator is constructed such that like the hydraulic drive system of the backhoe excavator, the right travel motor, left travel motor, swing motor, boom cylinder, arm cylinder and bucket cylinder can be operated in accordance with the operation of the right travel control pedal device, left travel control pedal device, swing control lever device, boom control lever device, arm control lever device and bucket control lever device and in addition, such that the open/close cylinder can be operated in accordance with the operation of the open control pedal device or close control pedal device.
As a further large hydraulic excavator constructed like the large backhoe excavator and large loader excavator mentioned above, there is one disclosed in JP-A-2004-100134.
It is to be noted that the kind of large hydraulic excavators to be manufactured is determined to that of those shipped more between backhoe excavators and loader excavators and such large hydraulic excavators may be kept in stock. Subsequently, each large hydraulic excavator is transported in a divided condition to a work site where digging work or the like is to be performed, and is then assembled into the type ordered by the customer. The type of hydraulic excavator ordered by each customer may be different from that of a hydraulic excavator manufactured or kept in stock. As a consequence, it becomes necessary to change the type of the hydraulic excavator from a backhoe excavator to a loader excavator or from a loader excavator to a backhoe excavator in the assembly stage of the hydraulic excavator. When changing the type of a hydraulic excavator as mentioned above, the progress of work at the work site will be substantially delayed from the work schedule if the change is dealt with by doing the fabrication and transportation again from the beginning with respect to all the components of the hydraulic excavator. Accordingly, the change of the hydraulic excavator is conducted by using as many components as possible from the hydraulic excavator before the change, and the thus-changed hydraulic excavator is then delivered.
When changing a hydraulic excavator, which is to be used at a work site, from a backhoe excavator to a loader excavator, for example, the travel base and swing upperstructure and the components of the hydraulic drive system, said components being associated with these travel base and swing upperstructure, that is, the right travel control pedal device, left travel control pedal device, swing control lever device, boom control lever device, arm control lever device and bucket control lever device, all of which exist as components of the backhoe excavator, can be used as they are, and an open control pedal device and a close control pedal device are newly arranged. The front working assembly is replaced by a front working assembly for a loader excavator, and following this replacement, the boom cylinder, arm cylinder and bucket cylinders are also replaced by those corresponding to the loader excavator. An open/close cylinder which is not arranged in the front working assembly for the backhoe excavator is attached to the bucket. Further, the components of the hydraulic drive system, said components being associated with the front working assembly, are modified such that the replaced boom cylinder, arm cylinder and bucket cylinder can be operated in accordance with operation of the existing right travel control pedal device, existing left travel control pedal device, existing swing control lever device, existing boom control lever device, existing arm control lever device and existing bucket control lever device and also, such that the newly-arranged open/close cylinder can be operated in accordance with operation of the newly-arranged open control pedal and newly-arranged close control pedal.